A prior art will be described below. An example of a valve device which is turned by an arm will be described with reference to FIG. 7B. In this regard, in the prior art, a same part as a functional part in embodiments to be described later will be denoted by a same reference character. In a valve device shown in FIG. 7B, an opening/closing valve 13 is supported by a tip of a valve arm 12 which is turned. The opening/closing valve 13 is a valve in which a valve body 16, which is formed in a shape of a nearly circular plate, is integrated with a valve-side combined part 18, which is a supported by the valve arm 12. The valve-side combined part 18 is formed in a shape of a shaft shaped like a circular column.
Issues of the prior art will be described below. A height dimension H of the opening/closing valve 13 is made a dimension obtained by adding a height dimension h2 of the valve-side combined part 18 to a thickness dimension h1 of the valve body 16. The height dimension H of the opening/closing valve 13 is required to be shortened for the purpose of reducing a size of the valve device and reducing a pressure loss or the like when the opening/closing valve 13 is opened. In other words, the thickness dimension h1 of the valve body 16 is required to be thinned and the height dimension h2 of the valve-side combined part 18 is required to be shortened.
However, when the opening/closing valve 13 is closed, a valve closing load is applied to a center of the valve body 16, so that a stress is caused in the valve body 16 in a direction in which an outer peripheral side of the valve body 16 is warped. For this reason, in order to secure a strength of the valve body 16, it is difficult to thin the valve body 16. In other words, in a two-step structure in which “the height dimension h2 of the valve-side combined part 18” is added to “the thickness dimension h1 of the valve body 16”, it is difficult to shorten the height dimension H of the opening/closing valve 13, so that it is impossible to reduce the height dimension of the opening/closing valve and to increase the strength of the valve body at the same time.